1. Technical Field
The present invention relates to thermoset polyester resin-containing materials, and more particularly, relates to the employment of flexibility modifying agents in a polyester resin system to improve the aesthetic, surface and dynamic impact properties of the polyester resin system over existing polyester resin systems.
2. Background and Description of the Related Art
Polyester resin systems such as sheet molding compounds ("SMC") are popularly employed in many commercially important materials. Generally, these systems include a reinforcement material such as glass. The materials thus tend to be relatively rigid. While such rigidity often is desirable, in some instances it limits the practical utility of the material. For instance, SMC materials find popular application as exterior body panels for transportation vehicles, such as automobiles. At present SMC materials advantageously are employed as exterior horizontal body panels (e.g., roofs, hoods and deck lids) in the automotive industry. The rigidity of SMC, however, limits its usefulness as an exterior vertical body panel. Of course, by "exterior horizontal body panel", as used herein, is meant an exterior body panel that is generally disposed in a substantially horizontal position, relative to the ground, in an assembled vehicle. Likewise, by "exterior vertical body panel", as used herein, is meant an exterior body panel (such as a door, fender or a quarter panel) that is disposed in a generally vertical position relative to the ground, in an assembled vehicle. Accordingly, until the present invention, there has been a need for a sheet molding compound material that can be easily molded to form articles having good flexibility characteristics, good impact (e.g. stone-chip damage) resistance, relatively good strength with reduced levels of glass content, a commercially desirable specific gravity, good surface finish and good thermal expansion characteristics.
It has been suggested in the art to modify particular molding compounds using specific modifiers or combinations of modifiers to alter the characteristics of the molding compounds in one or more of the above ways. In this regard, various formulations are disclosed in U.S. Pat. Nos. 4,839,431, 4,808,361, 4,745,018, 4,534,888, 4,400,478, 4,329,438, 4,076,767 and 3,887,515, all of which are hereby incorporated by reference.
Other additives that may be employed in a plastic material are disclosed in U.S. Pat. No. 4,663,388, which is incorporated herein by reference.